The innovative membrane-based technology called reverse electrodialysis (RED) is capable of producing electrical power from the controlled mixing of two aqueous streams of different salinity. There has been tremendous progress so far in the development of RED process in terms of system development, spacer design, membranes properties and operational conditions optimization. Among those, characteristics of the ion exchange membranes are found to be the critical element affecting the performances of RED process. In this respect, a brief overview of the latest developments in ion exchange membranes were presented in this review, focussing on their properties and performances in RED applications. The recent developments of nanocomposite and ion selective membranes, particularly pore filling ion exchange membranes due to their high performances and inexpensive fabrication cost were also summarized. Shortly, fouling problem for the ion exchange membranes employed in the RED system was mentioned.

Polyethersulfone (PES) membrane can be easily fouled during wastewater treatment as it is slightly hydrophobic. Consequently, several modifications are required to improve membrane surface properties to avoid membrane fouling. UV irradiation and cross-linked polyvinyl alcohol coating on nanohybrid membranes were performed in this study, and PES was combined with ZnO nanoparticles as an inorganic additive. Also, the PES-ZnO nanohybrid membrane was treated under the UV irradiation for a specific exposure time followed with membrane coating using polyvinyl alcohol (PVA) by the dip-coating method. Then, rubber wastewater filtration tests were performed using a cross-flow filtration system. The results revealed that the modifications significantly improved permeability and selectivity. As the duration of the UV irradiation increased, the higher mean flux value increased up to 14.55 L.m-2.h-1, but it was sacrificing the rejection efficiency. While the PVA coating decreased the water permeability up to 10.5 L.m-2.h-1 and increased the PVA concentration, the contaminant rejection increased up to 82%. The best membrane composition based on this study consisted of 17 wt.% of PES, 1 wt.% of ZnO nanoparticles, 5 wt.% Polyethylene glycol (PEG), 2 minutes UV irradiation, and 3% PVA coating.

This research investigated stability of two novel aminated polyphenylene polymers as anion exchange layers in bipolar membranes. Bipolar membrane stability was tested under operating conditions of 50 mA/cm2, and under conditions of soaking in room temperature 1 M NaOH. The stability of the custom made bipolar membranes was compared with those for two commercial membranes. For the polyphenylene-based membranes, there was no measurable increase in operating voltage when run continuously at a current density of 50 mA/cm2. For the two commercial membranes, the operating voltages increased by 3.2 to 4.4 mV per day when operated continuously over an 85 day testing period. Commercial membrane degradation in 1 M NaOH was similar to that under real operating conditions, with average rates of voltage increase of 3.2 to 3.5 mV/d. The custom made membrane containing a quaternary ammonium-tethered poly(biphenylalkylene) (PBPA) anion exchange layer did not show any loss in performance in either stability test. Density functional theory (DFT) simulations were used to calculate activation barriers and reaction energies for nucleophilic attack on the polymer backbones and cation functional groups on each of the four anion exchange polymers. Cation loss from all four polymers was thermodynamically favorable, with activation barriers ranging from 64 to 138 kJ/mol. The two commercial polysulfone-based anion exchange membranes were susceptible to cleavage of the ether bonds. However, the polyphenylene-based anion exchange polymers were considerably more stable with respect to backbone cleavage. The DFT calculations showing that the PBPA polymer was the most stable confirmed the results of the stability tests.

The total volume of water on Earth is circa 300 million cubic miles, with close to 98.0% being salt water and the remaining 2.0% fresh water. It has been increasingly more challenging to harvest fresh water from surface water, seawater and even from wastewater due to the combination of factors, viz. burgeoning population growth, rapid industrialization and climate change. Recently, membrane distillation (MD) emerges as a promising cost-effective thermal driven sustainable water recovery technology when integrated with renewable energy sources. However, one of the major challenges for MD is the membrane fouling, which has been gaining popularity in the recent literature, as well. The membrane fouling propensity for MD is very much depends on the type of feed water, suitability of membrane and the operating conditions. The objective of this review is to investigate the fouling phenomena of membrane distillation in wastewater treatment and desalination. The design of membrane and its system from the perspective of material and process design were discussed to provide an insight on the current and future advancement in MD technology for water recovery. Finally, the future trend of MD is projected based on the state of the art development of MD process.

In this study, a time-dependent 2D axisymmetric model of a multilayer hollow fiber composite membrane for gas separation is proposed. In spite of the common multilayer membranes, which a dense layer coated on a porous support layer and subjected into the feed stream, here, the porous support is exposed to the feed gas. In this regard, the governing equations of species transport are developed for model domains and then solved by a finite element method (FEM). Gas permeation properties of pure H2 , O2 , N2 , CH4 , CO2 and He are calculated and validated with experimental data with good conformity. Obtained results indicate that with increasing the temperature, the permeability and diffusion coefficient increased while the solubility decreased. Moreover, the permeability and solubility variations with temperature for a heavier gas, CO2 , were higher than those for the lighter ones, while the diffusion coefficient variation with temperature for the lither gas, such as He, was more than the heavier ones. By increasing the CO2 feed stream temperature from 25 to 75°C, its permeability and diffusion coefficient increased respectively from 245 to 307 Barrer and from 205 to 282×10-12 m2 /s, while the CO2 solubility decreased from 0.85 to 0.76 cm3.cm3.bar1. In the case of He and for the same temperature variation range, its permeability and diffusion coefficient increased respectively from 39 to 42 Barrer and from 2180 to 2834 10-12 m2 /s, while the solubility of He decreased from 0.013 to 0.011 cm3 .cm-3.bar-1.

In this work we report the experimental assessment of the performance of a new catalytic hollow fiber reactor with supported Pd catalyst for nitrite removal from polluted waters. The reactor configuration facilitates working at low flowrate and hydrogen concentrations in order to improve the selectivity of the reduction reaction towards nitrogen, thus, inhibiting the formation of ammonia. Pd catalyst was supported on propylene and polyethersulfone hollow fibers following a simple impregnation method; the stability of the supported catalyst was checked along the operation time. Experiments of nitrite reduction were carried out in the range of 0.075-1 bar of H2 partial pressure, 0.3-0.4 bar of CO2 partial pressure, 200-400 mL/min of water flowrate and 20-200 mL/min of gas flowrate with an initial nitrite concentration of 150 mg/L. Under the experimental conditions a selectivity to N2 close to 90% with 80% conversion of nitrites was achieved.

Sulfoanted poly(ether ether ketone) membranes were prepared by the sulfonating agent sulfuric acid. These membranes were modifed by incorporating conducting polymer polypyrrole in order to increase the ionic conductivity and reduce the methanol transmission rate. The modifed composite membranes were then compared on the basis of ionic conductivity, methanol transmission rate and thermal stability. Results indicated that the new membranes were thermally stable up to 300oC and gave moderate ionic conductivity. Consequently, composite membranes show less water uptake and swelling. The composite membranes were then characterized by FT-IR spectroscopy, Differential Scanning Calorimetry (DSC), Thermogravimetric analysis (TGA), and ionic conductive properties were evaluated by Electrochemical Spectroscopy Impedance.

The performances of the optimized tree-type cylindrical-shaped nanoporous fltering membranes with six or seven branch pores in each pore tree are analytically studied. The radius Rb,1 of the branch pore for fltration is normally on the 1 or 10 nm scales. The larger trunk pore is for improving the flux of the membrane. For liquid-particle separations, the radius Rb,1 of the branch pore is determined by the particle size, and the radius Rb,2 of the trunk pore is optimized for yielding the lowest flow resistance of the membranes; The optimum ratios of Rb,2 to Rb,1 are typically calculated respectively for weak, medium-level and strong liquid-pore wall interactions when the operational parameter values are widely varied. The capability of the liquid-liquid separation of these membranes is also analytically shown.